linux-kernel - [PATCH] mm/swap_state: Skip meaningless swap cache readahead when ra

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Message-ID: <20201009133059.58407-1-linmiaohe@huawei.com>
Date:   Fri, 9 Oct 2020 09:30:59 -0400
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     <akpm@...ux-foundation.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <linmiaohe@...wei.com>
Subject: [PATCH] mm/swap_state: Skip meaningless swap cache readahead when ra_info.win == 0

swap_ra_info() may leave ra_info untouched in non_swap_entry() case as page
table lock is not held. In this case, we have ra_info.nr_pte == 0 and it is
meaningless to continue with swap cache readahead. Skip such ops by init
ra_info.win = 1.

Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
---
 mm/swap_state.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/swap_state.c b/mm/swap_state.c
index ee465827420e..b9013c3f94c9 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -839,7 +839,7 @@ static struct page *swap_vma_readahead(swp_entry_t fentry, gfp_t gfp_mask,
 	swp_entry_t entry;
 	unsigned int i;
 	bool page_allocated;
-	struct vma_swap_readahead ra_info = {0,};
+	struct vma_swap_readahead ra_info = {1,};
 
 	swap_ra_info(vmf, &ra_info);
 	if (ra_info.win == 1)
-- 
2.19.1